Resin-sealed electrical device

ABSTRACT

Electrical elements constituting an electrical device are embedded into at least one layer of a finely divided insulating material which is formed within a case by filling the case with the insulating material. A low viscosity resin is poured into the case to be impregnated into said at least one layer of the insulating material and to form a cover layer covering the free surface of the top insulating cover layer. The resistances to moisture, vapor, shocks, vibration, cycling temperature change and so on are remarkably improved so that the highly reliable performances of the enclosed electrical device under severe environmental conditions may be ensured.

This is a continuation, of application Ser. No. 480,580 filed June 18, 1974 now abandoned.

BACKGROUND OF THE INVENTION

The present invention relates to electrical device of motor bicycles, snow mobiles, or other industrial machinery which are sealed with resins so that they may be satisfactorily used under severe environmental conditions such as vibrations and cycling change in temperature over a very wide range (hereinafter referred to as cycling temperature change).

Hitherto, in order to protect the electrical devices from the severe environments, especially from vibrations, moisture and vapor, and cycling temperature change, they are sealed or enclosed with highly flexible resins such as epoxy resins, urethane resins, and so on. However, when a flexible resin is used in order to protect the electrical devices at low temperatures, the resistance to heat is not satisfactory. On the other hand, when a resin which is satisfactorily resistant to heat is used, its resistance to low temperature is not satisfactory. That is, the resistance to heat and the resistance to low temperature are incompatible with each other. In order to overcome this problem, a mixture consisting of a flexible resin and an insulating material has been used to seal or enclose electrical devices so that the coefficient of thermal expansion may be minimized. However, when an insulating material is mixed into a resin, the viscosity of the mixture is increased so that the electrical device cannot be completely set and sealed with the mixture. Thus, the use of such mixture cannot attain the satisfactory sealing effects of the electrical devices in practice.

The present invention was therefore made in order to solve the above and other problems encountered in the prior art techniques. One of the objects of the present invention is to provide resin-sealed electrical devices which may satisfactorily function even when they are subjected to severe cycling temperature change, vibrations and high humidity. In the present invention, an electrical device is not sealed with a mixture consisting of a resin and an insulating material, but is sealed by being embedded in one or more layers of the insulatng material among the particles of which sinks into a resin of low-viscosity. However, the grain size of the insulating compounds to be used must not be too coarse or too fine. When the grain size is too fine, it becomes very difficult to impregnate a resin from the top surface of an insulating material layer and as a result the impregnation time becomes inevitably longer. On the other hand, if the grain size is too coarse, the impregnated resin does not come short of the electrical elements constituting an electrical component. Therefore, when the electrical device is subjected to cycling temperature change cracks occur. It is of course easy to impregnate a resin into a layer of an insulating material of a coarse grain size. However, the grain size of the insulating material must be determined so that the desired electrical characteristics and performance of the resin-sealed electrical devices may be maintained.

Briefly stated, the present invention provides a resin sealed electrical device comprising an electrical element, a case for housing said electrical device therein, a layer of an insulating compound such as finely divided quartz (SiO₂), magnesium oxide (MgO), lead oxide (PbO), borosilicate soda glass or rubber so that said electrical component may be embedded in said layer, and a cover layer consisting of a resin of low viscosity formed over said first mentioned layer, said resin of low viscosity being impregnated into said first mentioned layer.

According to one aspect of the present invention, an electrical component is embedded into a layer of a finely divided insulating material charged into a case, and a resin of low viscosity is poured into the case so that it may be impregnated into the insulating material layer and may form a cover layer over the free surface of the insulating material layer. Therefore, the resistance to moisture and vapor of the electrical device may be considerably improved, so that the deterioration of the electrical characteristics may be well prevented. Furthermore, the commercial value of the electrical device may be remarkably increased. Moreover, the performance of the electrical device sealed with resin in accordance with the present invention is very satisfactory under very severe environmental conditions; no crack is started; and the desired electrical characteristics may be maintained. According to another aspect of the present invention, the particles of different sizes of an insulating component are used so that a plurality of insulating material layers of different grain size ranges may be formed. Therefore, the impregnation of a resin of low viscosity is readily accomplished within a short time, so that the fabrication efficienty of the electrical device may be much improved.

The above and other objects, features and advantages of the present invention will become more apparent from the following description of some preferred embodiments and examples thereof in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are a schematic top and a sectional view of a conventional testing washer which is shown as an example of electrical elements constituting an electrical component according to the present invention;

FIG. 3 is a sectional view of the washer shown in FIGS. 1 and 2 and sealed with a resin in accordance with the present invention;

FIGS. 4 and 5 are a top and a sectional view, respectively, of an electrical component, i.e. semiconductor device of a condensor discharge type ignition device to be sealed with resin in accordance with the present invention; and

FIG. 6 is a sectional view thereof sealed in accordance with the present invention.

FIRST EMBODIMENT, FIGS. 1 - 3

The first embodiment of the present invention will be described in conjunction with a sample, i.e., a conventional "Olyphant" washer generally designated by 1 in FIGS. 1 - 3. The washer 1 (9 mm in diameter and 6.5 mm in height) has eight projections 2 (2.5 mm in height) protruded from both surfaces thereof. The washer 1 is embedded into a layer of an electrical insulating material 4 charged into an aluminum case 3 (50 mm in diameter and 30 mm in depth) as shown in FIG. 3. A resin of a low viscosity (whose viscosity is less than 1500^(CP) at room temperature) is directly impregnated into the layer 4 and is poured into the aluminum case 3 so that a cover layer 5 whose thickness is thinner than that of the insulating material layer 4 may be formed over the free surface of the layer 4.

Next some examples obtained by the above described method will be described.

EXAMPLE 1

Finely divided quartz SiO₂ was used as an insulating material. The degree of impregnation depending upon the grain sizes of resins of low viscosity and the appearance of the samples after they were subjected to the cycling temperature change tests were investigated. The results are shown in Tables 1 and 2.

                                      TABLE 1                                      __________________________________________________________________________         Average grain              Results of cycling                                  size in micron       Impregna-                                                                            temperature change                              Sample                                                                             of insulating                                                                          Constituent of low                                                                          tion  test in aluminum                                No. material (SiO.sub.2)                                                                   viscosity resin                                                                             property                                                                             casing                                          __________________________________________________________________________     1    44                  poor  good                                            2    61     Resin: bisphenol type                                                                       good  good                                            3    88     epoxy resin  good  good                                            4   149     Hardener: methyl highmic                                                                    good  good                                            5   177     acid anhydride                                                                              good  good                                            6   250     Diluent: polypropylene                                                                      good  good                                            7   350     glycol       good  good                                            8   500     Viscosity: 600 - 800.sup. cp                                                                good  good                                            9   840                  good  good                                            10  1680                 good  good                                            11  2830                 good  good                                            12  3360                 good  good                                            13  4760                 good  good                                            14  5660    Resin:   "   good  poor (cracks appear                                         Hardener:   "      after 4 cycles)                                 15  conglomerated                                                                          Diluent:   " good  poor (cracks appear                                         Viscosity:   "     after 1 cycle)                                  __________________________________________________________________________      (Cycling temperature change test: One cycle consists of three steps of         leaving samples for one hour at -65° C., leaving the samples for        five minutes at room temperature and leaving the samples for one hour at       155° C.)                                                          

                                      TABLE 2                                      __________________________________________________________________________         Average grain              Results of cycling                                  size in micron       Impregna-                                                                            temperature change                              Sample                                                                             of insulating                                                                          Constituent of low                                                                          tion  test in aluminum                                No. material (SiO.sub.2)                                                                   viscosity resin                                                                             property                                                                             casing                                          __________________________________________________________________________     16   88     Resin: bisphenol type                                                                       good  good                                                        epoxy resin                                                        17  149     Hardener: aliphatic                                                                         good  good                                                        amine                                                              18  350                  good  good                                            19  500     Diluent: polypropylene                                                                      good  good                                                        glycol                                                                         Viscosity: 600 - 800.sup. cp                                       20  2830                 good  good                                            21  4760                 good  good                                            __________________________________________________________________________      (Cycling temperature change test: One cycle consists of three steps of         leaving samples for one hour at -65° C., leaving the samples for        five minutes at room temperature and leaving the samples for one hour at       155° C.)                                                          

It is seen that when the average grain size of the insulating materials is between 61 μ and 4760 μ, the degree of impregnation of the resins of low viscosity is better and the results of the cycling temperature change tests were also better. Other insulating materials such as magnesium oxide MgO, ferric oxide Fe₂ O₃, lead oxide PbO, hollow borosilicate soda glass and rubber which have the same average grain size as the above-mentioned were also tested. The degree of impregnation as well as the results of the cycling temperature change tests were better.

EXAMPLE 2

The upper and lower layers of finely divided quartz SiO₂ of different grain sizes were formed in the case so that electrical elements were embedded therein. An epoxy resin of low viscosity was impregnated into the upper and lower layers. The degree of impregnation as well as the results of the samples subjected to the cycling temperature change tests were investigated. The results are shown in Table 3.

                                      TABLE 3                                      __________________________________________________________________________     Average grain                                                                  size in micron                                                                 of insulating                  Results of cycling                              material (SiO.sub.2)     Impregna-                                                                            temperature change                              Sample                                                                             upper                                                                              lower                                                                              Constituent of low                                                                          tion  test in aluminum                                No. layer                                                                              layer                                                                              viscosity resin                                                                             property                                                                             casing                                          __________________________________________________________________________     22  149 840              good  good                                            23  177 840              good  good                                            24  350 840 Resin: bisphenol type                                                                       good  good                                                        epoxy resin                                                        25  840 149              good  good                                            26  840 177 Hardener: aliphatic                                                                         good  good                                                        amine                                                              27  840 350 Diluent: polypropylene                                                                      good  good                                                        glycol                                                             28  350 2830             good  good                                            29  500 2830                                                                               Viscosity: 400 - 600.sup. cp                                                                good  good                                            30  840 2830             good  good                                            __________________________________________________________________________      (Cycling temperature change test: One cycle consists of three steps of         leaving samples for one hour at -65° C., leaving the samples for        five minutes at room temperature and leaving the samples for one hour at       155° C.)                                                          

It is seen that both the degree of impregnation and the results of the cycling temperature change tests were better even when the two layers of the insulating material, finely divided quartz SiO₂, of different grain sizes were formed. Furthermore, the degree of impregnation was improved and the impregnation time was reduced because of the two layers of the insulating material of different grain sizes. Other insulating material such as magnesium oxide MgO, ferric oxide Fe₂ O₃, lead oxide PbO, hollow borosilicate soda glass and rubber were also tested. The results were quite satisfactory.

EXAMPLE 3

Finely divided quartz was charged so as to form three layers of different grain sizes. Electrical elements were embedded into an intermediate layer of finest grain sizes. The upper and lower layers had the grain sizes greater than that of the intermediate layer. An epoxy resin of low viscosity was impregnated into these layers. The results of the impregnation tests and the cycling temperature change tests are shown in Table 4.

                                      TABLE 4                                      __________________________________________________________________________     Average grain size in                                                          micron of insulating                                                           material (SiO.sub.2)                Results of cycling                                 inter-                Impregna-                                                                            temperature change                         Sample                                                                             upper                                                                              mediate                                                                             lower                                                                              Constituent of low                                                                          tion  test in aluminum                           No. layer                                                                              layer                                                                               layer                                                                              viscosity resin                                                                             property                                                                             casing                                     __________________________________________________________________________     31  1680                                                                               88   350 Resin: bisphenol type                                                                       good  good                                                        epoxy resin                                                                    Hardener: aliphatic                                           32  350 80   1680                                                                               amine        good  good                                                        Diluent: polypropylene                                                         glycol                                                        33  840 177  840 Viscosity: 400 - 600 .sup.cp                                                                good  good                                       __________________________________________________________________________      (Cycling temperature change test: One cycle consists of three steps of         leaving samples for one hour at -65° C., leaving the samples for        five minutes at room temperature and leaving the samples for one hour at       155° C.)                                                          

It is seen that both the degree of impregnation and the results of the cycling temperature change tests were satisfactory even when the three layers of the insulating material, finely divided quartz SiO₂, of different grain sizes were formed. The impregnation time was also reduced. The results of the tests of other insulating material such as magnesium oxide MgO, ferric oxide Fe₂ O₃, lead oxide PbO, hollow borosilicate soda glass and rubber were also satisfactory.

SECOND EMBODIMENT, FIGS. 4 - 6

In the second embodiment shown in FIGS. 4 - 6, an electrical component, i.e., a semiconductor device (CD amplifier) for a condenser discharge type ignition device for use with a motor bicycle is sealed with resin. That is, the semiconductor device comprises, as best shown in FIGS. 4 and 5, an aluminum case 6, a lead wire cover 7, a lead wire 8, grommets 9, a printed circuit board 10, a rubber bush 11 for a lead wire, electrical circuit elements 12, a semiconductor circuit complete 13. As shown in FIG. 6, an insulator or insulating material 15 is charged into the aluminum case 6 so that the electrical elements 10, 12 and 13 are embedded into the layer of the insulating material. Thereafter, a resin of low viscosity is impregnated into the layer of the insulating material 15 and is poured into the aluminum case 6 so that a cover layer 14 may be formed over the free surface of the insulating material layer. Thus, the electrical component is sealed with the resin. As best shown in FIG. 6, the thickness of the cover layer 14 is smaller than that of the insulating material layer.

EXAMPLE 4

As an example of electrical devices, semiconductor devices (CD amplifiers) for condenser type ignition devices for outboard engines were sealed with resins according to the method of the present invention and the prior art methods. After the resin-sealed semiconductor devices underwent the moisture and vapor tests and the cycling temperature change tests, their electrical characteristics performance and appearances were investigated. The results are shown in Table 5.

                                      TABLE 5                                      __________________________________________________________________________                                          Electrical                                                                     charac-                                                                 Appearance                                                                            teristics                                                               after cycling                                                                         after cycling                             A resin-sealed          Dampproof                                                                            temperature                                                                           temperature                                                                           Synthetic                          electrical device                                                                       Constituent of resin                                                                          test  change test                                                                           change test                                                                           decision                           __________________________________________________________________________     Prior Art 1                   cracks appear                                    (CD amplifier for                                                                       Resin:polyurethane                                                                            good  after one                                                                             inoperable                                                                            poor                               outboard engines)                                                                       resin                cycle                                            Prior Art 2                                                                             Resin:flexible epoxy foaming and                                      (CD amplifier for                                                                       resin          good  swelling after                                                                        inoperable                                                                            poor                               outboard engines)                                                                       Hardener: amines     one cycle                                                 Resin:flexible epoxy                                                  Prior Art 3                                                                             resin mixed with                                                      (CD amplifier for                                                                       silica         good  cracks appear                                                                         inoperable                                                                            poor                               outboard engines)                                                                       (25 parts hundred epoxy resin)                                                 Hardener: acid anhydrides                                             Prior Art 4                          good in                                   (CD amplifier for                                                                       silicone rubber                                                                               poor  good   operation                                                                             poor                               outboard engines)                                                              Electrical device                                                                       Resin:bisphenol A type                                                according to the                                                                        epoxy resin                                                           present invention                                                                       Hardener: acid anhydride                                                                      good  good   good in                                                                               good                               (CD amplifier for                                                                       Insulating material: SiO.sub.2                                                                             operation                                 outboard engines)                                                                        (grain size: 840μ)                                                Sample No. 34                                                                           Resin:bisphenol A type                                                         epoxy resin                                                                    Hardener: acid anhydride                                              "        Insulating material: SiO.sub.2                                        Sample No. 35                                                                            ##STR1##      good  good   good in operation                                                                     good                                        Resin:bisphenol A type                                                         epoxy resin                                                                    Hardener: acid anhydride                                              "        Insulating material: SiO.sub.2                                        Sample No. 36                                                                            ##STR2##      good  good   good in operation                                                                     good                               __________________________________________________________________________      (Dampproof test: Samples were left for 240 hours at humidity of 95 %)          (Cycling temperature change test: One cycle consists of three steps of         leaving samples for one hour at -65° C., leaving the samples for        five minutes at room temperature and leaving the samples for one hour at       155° C.)                                                          

The results of the tests of the semiconductor devices sealed with resins in accordance with the present invention were quite satisfactory, and it has been found that they may be satisfactorily used in the outboard engines.

EXAMPLE 5

As an example of electrical devices, semiconductor devices (DC amplifiers) of the condenser discharge type ignition devices for snowmobile engines were sealed with various insulating materials and resins, and were subjected to the moisture and vapor tests and the cycling temperature change tests. The results are shown in Table 6.

                                      TABLE 6                                      __________________________________________________________________________                                         Electrical                                                                     characteri-                                                             Appearance                                                                            stic after                                          Constituent of low  after cycling                                                                         cycling                                    A resin-sealed                                                                          viscosity resin and                                                                          Dampproof                                                                            temperature                                                                           temperature                                                                           Synthetic                           electrical device                                                                       insulating material                                                                          test  change test                                                                           change test                                                                           decision                            __________________________________________________________________________     Electrical device                                                                       Resin: bisphenol type                                                 according to the                                                                        epoxy resin                                                           present invention                                                                       Diluent: polypropylene     good in                                    (CD amplifier for                                                                       glycol        good  good   operation                                                                             good                                snow mobiles)                                                                           Hardener: aliphatic amine                                             Sample No. 37                                                                           Insulating material: SiO.sub.2                                                 (grain size: 420μ)                                                          Resin:   "                                                                     Diluent:   "                                                            "      Hardener:   "              good in                                    Sample No. 38                                                                           Insulating material:                                                                         good  good   operation                                                                             good                                         SiO.sub.2 + CaCO.sub.3 (30 parts)                                              hundred SiO.sub.2)                                                             (grain size: 420μ)                                                          Resin:   "                                                              "      Diluent:   "                                                          Sample No. 39                                                                           Hardener: K61-B (amine)                                                                      good  good   good in                                                                               good                                         Insulating material: SiO.sub.2                                                                            operation                                           (grain size: 420μ)                                                          Resin:   "                                                              "      Diluent:   "                                                          Sample No. 40                                                                           Hardener: aliphatic amine  good in                                             Insulating material:                                                                         good  good   operation                                                                             good                                         SiO.sub.2 + CaCO.sub.3 (30 parts                                               hundred SiO.sub.2)                                                             (grain size: 420μ)                                                   "      Resin: urethane resin                                                                        good  good   good in                                                                               good                                Sample No. 41                                                                           Insulating material: SiO.sub.2                                                                            operation                                           (grain size: 420μ)                                                 __________________________________________________________________________      (Dampproof test: Samples were left for 240 hours at humidity of 95 %)          (Cycling temperature change test: One cycle consists of three steps of         leaving samples for one hour at -65° C., leaving the samples for        five minutes at the room temperature and leaving the samples for one hour      at 155° C.)                                                       

The results were quite satisfactory, and it has been found that the semiconductor devices sealed with resins in accordance with the present invention may be satisfactorily used in the snowmobile engines.

EXAMPLE 6

As an example of electrical devices, non-contact voltage regulators for engines of agricultural machinery were sealed with various insulating materials and resins, and subjected to the moisture and vapor tests and the cycling temperature change tests. The results are shown in Table 7.

                                      TABLE 7                                      __________________________________________________________________________                                         Electrical                                                                     characteri-                                                             Appearance                                                                            stics after                                         Constituent of low  after cycling                                                                         cycling                                    A resin-sealed                                                                          viscosity resin and                                                                          Dampproof                                                                            temperature                                                                           temperature                                                                           Synthetic                           electrical device                                                                       insulating material                                                                          test  change test                                                                           change test                                                                           decision                            __________________________________________________________________________     Electrical device                                                                       Resin: bisphenol type                                                 according to the                                                                        epoxy resin                                                           present invention                                                                       Diluent: polypropylene                                                (non-contact volt-                                                                      glycol                     good in                                    age regulator for                                                                       Hardener: acid anhydride                                                                     good  good   operation                                                                             good                                agricultural                                                                            (MHAC)                                                                machinery)                                                                              Insulating material: SiO.sub.2                                        Sample No. 42                                                                           (grain size: 420μ)                                                          Resin:   "                                                                     Diluent:   "                                                            "      Hardener: aliphatic amine  good in                                    Sample No. 43                                                                           Insulating material:                                                                         good  good   operation                                                                             good                                         SiO.sub.2 + CaCO.sub.3 (30 parts)                                              hundred SiO.sub.2)                                                             (grain size: 420μ)                                                          Resin:   "                                                                     Diluent:   "                                                            "      Hardener: K61-B (amines)                                                                     good  good   good in                                                                               good                                Sample No. 44                                                                           Insulating material: SiO.sub.2                                                                            operation                                           (grain size: 420μ)                                                 __________________________________________________________________________      (Dampproof test: Samples were left for 240 hours at humidity of 95 %)          (Cycling temperature change test: One cycle consists of three steps of         leaving samples for one hour at -65° C., leaving the samples for        five minutes at room temperature and leaving the samples for one hour at       155° C.)                                                          

The results were quite satisfactory, and it has been found that the semiconductor devices sealed with resins in accordance with the present invention may be satisfactorily used in agricultural machinery engines.

EXAMPLE 7

As an example of electrical device, semiconductor devices (CD amplifiers) of the condenser dischage type ignition devices for motor bicycle engines were sealed with various insulating materials and resins and subjected to the moisture and vapor tests and the cycling temperature change tests. The results are shown in Table 8.

                                      TABLE 8                                      __________________________________________________________________________                                         Electrical                                                                     characteri-                                                             Appearance                                                                            stics after                                         Constituent of low  after cycling                                                                         cycling                                    A resin-sealed                                                                          viscosity resin and                                                                          Dampproof                                                                            temperature                                                                           temperature                                                                           Synthetic                           electrical device                                                                       insulating material                                                                          test  change test                                                                           change test                                                                           decision                            __________________________________________________________________________     Electrical device                                                                       Resin: bisphenol type                                                 according to                                                                            epoxy resin                                                           present invention                                                                       Diluent: polypropylene     good in                                    (CD amplifier for                                                                       glycol        good  good   operation                                                                             good                                motor bicycles)                                                                         Hardener: aliphatic amine                                             Sample No. 45                                                                           Insulating material: SiO.sub.2                                                 (grain size: 840μ)                                                          Resin   "                                                               "      Diluent:   "               good in                                    Sample No. 46                                                                           Hardener: K61-B (amines)                                                                     good  good   operation                                                                             good                                         Insulating material:   "                                                       (grain size: 840μ)                                                          Resin:   "                                                                     Diluent:   "                                                            "      Hardener:   "              good in                                             Insulating material:                                                                         good  good   operation                                                                             good                                Sample No. 47                                                                           SiO.sub.2 + CaCO.sub.3 (30 parts                                               hundred SiO.sub.2 )                                                            (grain size: 840μ)                                                 __________________________________________________________________________      (Dampproof test: Samples were left for 240 hours at humidity of 95 %)          (Cycling temperature change test: One cycle consists of three steps of         leaving samples for one hour at -65° C., leaving the samples for        five minutes at room temperature and leaving the samples for one hour at       155° C.)                                                          

As a result, it has been found that both the appearance and the electrical properties of the semiconductor devices sealed with resins are quite satisfactory.

EXAMPLE 8

As an example of electrical devices, semiconductor devices (CD amplifiers) of the condenser discharge type ignition devices for the snowmobile engines were sealed with hollow borosilicate soda glass, and subjected to the moisture and vapor tests and the cycling temperature change tests in order to investigate their electrical characteristics and appearance. The results are shown in Table 9.

                                      TABLE 9                                      __________________________________________________________________________                                         Electrical                                                                     characteri-                                                             Appearance                                                                            stics after                                         Constituent of low  after cycling                                                                         cycling                                    A resin-sealed                                                                          viscosity resin and                                                                          Dampproof                                                                            temperature                                                                           temperature                                                                           Synthetic                           electrical device                                                                       insulating material                                                                          test  change test                                                                           change test                                                                           decision                            __________________________________________________________________________     Electrical device                                                                       Resin: bisphenol type                                                 according to the                                                                        epoxy resin                                                           present invention                                                                       Diluent: polypropylene     good in                                    (CD amplifier for                                                                       glycol        good  good   operation                                                                             good                                snow mobiles)                                                                           Hardener: aliphatic amine                                                      Insulating material: hollow                                           Sample No. 48                                                                           borosilicate soda glass                                                        (grain size: 65μ)                                                           Resin:   "                                                              "      Diluent:   "               good in                                    Sample No. 49                                                                           Hardener:   " good  good   operation                                                                             good                                         Insulating material:   "                                                       (grain size: 840μ)                                                 __________________________________________________________________________      (Dampproof test: Samples were left for 240 hours at humidity of 95 %)          (Cycling temperature change test: One cycle consists of three steps of         leaving samples for one hour at -65° C., leaving the samples for        five minutes at room temperature and leaving the samples for one hour at       155° C.)                                                          

As a result, it has been found that both the appearance and the electrical properties of the semiconductor devices sealed with resins are quite satisfactory even when hollow borosilicate soda glass is used as insulating material, and that such semiconductor devices may be practically used in the snowmobile engines.

EXAMPLE 9

As an example of electrical devices, semiconductor devices (CD amplifiers) of the condenser discharge type ignition devices for the snowmobile engines were sealed with the insulating material consisting of finely divided rubber, and were subjected to the moisture and vapor tests and the cycling temperature change tests in order to investigate the electrical characteristics and appearance after the tests. The results are shown in Table 10.

                                      TABLE 10                                     __________________________________________________________________________                                         Electrical                                                                     characteri-                                                             Appearance                                                                            stics after                                         Constituent of low  after cycling                                                                         cycling                                    A resin-sealed                                                                          viscosity resin and                                                                          Dampproof                                                                            temperature                                                                           temperature                                                                           Synthetic                           electrical device                                                                       insulating material                                                                          test  change test                                                                           change test                                                                           decision                            __________________________________________________________________________     Electrical device                                                                       Resin: bisphenol type                                                 according to the                                                                        epoxy resin                                                           present invention                                                                       Diluent: polypropylene                                                (CD amplifier for                                                                       glycol                     good in                                    snow mobiles)                                                                           Hardener: aliphatic amine                                                                    good  good   operation                                                                             good                                         Insulating material: natural                                          Sample No. 50                                                                           rubber                                                                         (grain size: 1000μ)                                                         Resin:   "                                                                     Diluent:   "                                                            "      Hardener:   "              good in                                    Sample No. 51                                                                           Insulating material: silicon                                                                 good  good   operation                                                                             good                                         rubber                                                                         (grain size: 1000μ)                                                __________________________________________________________________________      (Dampproof test: Samples were left for 240 hours at humidity of 95 %)          (Cycling temperature change test: One cycle consists of three steps of         leaving samples for one hour at -65° C., leaving the samples for        five minutes at room temperature, and leaving the samples for one hour at      155° C.)                                                          

As a result, it has been found that both the electrical characteristics and the appearance of the semiconductor devices sealed with resins are quite satisfactory even when rubber is used as insulating material, and that such semiconductor devices may be practically used in the snowmobile engines. 

What we claim is:
 1. In a resin sealed electrical device comprising a case, a layer of finely divided insulating material and electrical elements both retained within said case and a resinous cover layer sealing said case,the improvement of providing a weather-resistant and shock-resistant device comprising using a finely-divided insulating layer having a grain size between about 61 and 4760 microns in size, in combination with a low viscosity resin cover layer which resin is at least partially impregnated into the finely divided insulating layer securing and retaining the insulating layer within said case and forming a weather-resistant cover layer sealing said case and the insulating layer and electrical elements contained therein.
 2. A resin-sealed electrical device according to claim 1, wherein said electrical elements are semiconductor parts of an amplifier for a condenser discharge type ignition device, and said resin of low viscosity is an epoxy type resin.
 3. The weather-resistant resin-sealed electrical device of claim 1 wherein the case contains a plurality of insulating layers each such layer comprising finely pulverized quartz, magnesium oxide, ferric oxide, lead oxide, hollow borosilicate soda glass, rubber or mixtures thereof. 